Comparative study of different mixing strategies in small high throughput experimentation reactors

The use of eccentric agitation, where the impeller is placed away from the centreline axis, was examined as a means of obtaining effective mixing in overhead-stirred unbaffled vessels used as high throughput experimentation (HTE) reactors. The performance was compared with conventional baffled and unbaffled configurations where the impeller was positioned at the vessel axis. Three vessels of diameters 35, 45 and 60 mm were used which comprehensively covers the HTE scale of interest. Power input per unit volume was maintained at a constant 168 W m(-3) for all experiments and water was used as the working fluid. Gross flow circulation and mixing times were determined by use of particle image velocimetry and planar laser induced fluorescence, respectively. The spatial distribution of turbulent kinetic energy within the vessels was determined to be independent of scale. However, local values of the turbulent kinetic energy within the spatial distribution were found to be scale-dependent. Mixing time has been found to be a function of vessel diameter, with the smaller vessels shown to be more efficient mixers. Energy dissipation within the vessels was estimated using a sub-grid scale closure model. The Smagorinsky SGS closure model was selected in preference of traditional estimation models, however all the models used gave a poor prediction of energy dissipation for the flow conditions studied. (c) 2005 Elsevier Ltd. All rights reserved.